Today, the new president of Iran vowed to follow the path of moderation and justice, not extremism. Hasan Rowhani talked of enhancing mutual trust between Iran and other countries. That marks a stark change in rhetoric from that of outgoing President Mahmoud Ahmadinejad. Rowhani campaigned as a reformist. He's also a cleric and Iran's former chief nuclear negotiator, who became known as the Diplomat Sheikh.

For more on what Rowhani's election means for Iran and for U.S.-Iranian relations, I'm joined now by Vali Nasr, dean of the Johns Hopkins School of Advanced International Studies. Professor Nasr, welcome to the program.

VALI NASR: Thank you.

BLOCK: Hasan Rowhani caught a lot of people by surprise. He didn't just win, he won really big - got over 50 percent of the vote and trounced the other candidates. What do you see as the message of his election?

NASR: Well, the message is that people of Iran are repudiating the legacy of Ahmadinejad. And that's quite important; that the Iranian public wants a different direction for the country and that the United States and the international community should not look at Iran through the prism of Ahmadinejad's legacy.

BLOCK: At the same time, though, ultimate authority rests with Iran's Supreme Leader, right, Ayatollah Khamenei? So how does Rowhani navigate that relationship?

NASR: With great difficulty. Iran's political system is complicated. There is a representative parliament. The president is elected. But then the Supreme Leader, who's unelected and unaccountable to the constitution, wields all the power. Rowhani would have to walk a tightrope between what he has proclaimed he wants to do - engagement, moderation, opening up the political system - and the authority of the Supreme Leader, which stands in his way.

BLOCK: You wrote in a blog post in Foreign Policy that the selection of Rowhani's is a game changer, in your words, for the United States. How would you expect the U.S. to engage with this new Iranian president? What might an opening gambit be?

NASR: Well, I think the United States' position on Iran has been very much laid by the rhetoric and the style of its previous president. So there is an opening here and the United States has to give Rowhani more than it was willing to give Ahmadinejad. Ultimately, if we treat Rowhani exactly the same way as we did Ahmadinejad, then that's a powerful message.

BLOCK: What know of Rowhani's style as a nuclear negotiator?

NASR: Well, what we know is that he was more forward-leaning than his successors. He is the only nuclear negotiator to sign on to a concession to the West, which was a voluntary suspension of uranium enrichment as a confidence-building measure, pending a broader deal. That's the good news.

The bad news is that he failed to translate that into a real deal. And he was badly burned domestically in Iran when he was blamed for having been weak, vis-a-vis the West, for having given away too much, for having opened the door for greater Western pressure on Iran. He was sacked from his job and he was excoriated. And therefore, I think he will be more cautious than we might expect in sticking his neck out with another concession to the United States and the international community.

BLOCK: Well, if the United States wants to strengthen the hand of reformists in Iran further, how does it proceed? And does it run the risk of closer ties with our country backfiring?

NASR: Well, there's always risk in diplomacy. But clearly, reformists would only be strengthened in Iran if they can show that they can get from the United States and international community something at the negotiating table that Ahmadinejad and the conservatives could not. And that means that we have to be willing to put on the table the possibility of lifting real sanctions that were never on the table before, in exchange for Iranian concessions.

Even being willing to consider them means that Rowhani will be starting the negotiation process with a stronger hand and a signal to the regime and the Iranian public would be that we actually do differentiate between hard-line conservatives and more moderate reformists.

BLOCK: Vali Nasr, thanks so much for talking with us today.

NASR: Thank you.

BLOCK: Vali Nasr is dean of the School of Advanced International Studies at Johns Hopkins. Transcript provided by NPR, Copyright NPR.